Recently, an ultraviolet sensor which performs ultraviolet detection using an Si substrate formed on an insulating substrate uses a lateral PIN diode with a comb-shaped ultraviolet detection part (see, Japanese Patent Application Laid-Open No. 64-2377 and Japanese Patent No. 3471394). The lateral PIN diodes disclosed in these patent documents have a structure in which a PN junction is formed in the Si substrate.
Meanwhile, there is proposed a semiconductor image sensor in which the surrounding of an ultraviolet photosensitive element is covered with a light shielding member, formed of a conductor, to shield oblique incident light (for example, Japanese Patent Application Laid-Open No. 2006-237576).
However, although the ultraviolet sensor having a comb-shaped lateral PIN diode can realize the increasing of a depletion region in the ultraviolet detection part and the improvement of the sensitivity in comparison with a linear diode, the sensitivity may be degraded depending on the incident angle of the incident light entering into the depletion region. Namely, when the incident angle is shallow, the attenuation length of the incident light from entering into the depletion region to be attenuated is increased, and therefore, the ultraviolet sensor responds to the light having a wavelength in a visible light region. Specifically, as shown in FIG. 11, when the attenuation length until the light having a wavelength of 400 nm is attenuated is about 100 nm, and when the attenuation length is larger than 100 nm, the ultraviolet sensor responds to blue visible light.
When the surrounding of the ultraviolet photosensitive element is covered only with the light-shielding member, even if the film thickness of a layer with a photosensitive element is formed therein is reduced, the attenuation length becomes larger than 100 nm depending on the incident angle of the incident light entering the photosensitive element, and the ultraviolet sensor may respond to a wavelength in a visible light region in some cases. Specifically, when the length (attenuation length) until the incident light entering at an incident angle of θ° enters an Si layer 82 and thereafter to abut against an insulating layer 84 is more than 100 nm as shown in FIG. 12, the ultraviolet sensor responds to visible light as shown in FIG. 11. FIG. 13 shows the relation between the incident angle of the incident light in the case in which the film thickness of the Si layer is 30 nm and the actual value of the Si film thickness with respect to the incident angle. As seen in FIG. 13, if the actual value of the Si film thickness is not more than 100 nm, the incident light at an incident angle of 18° or more can enter. There is no problem when there is a clear relation between the incident angle of the incident light and the film thickness of the Si layer. However, when this relation is unclear, there may arise a problem that the photosensitive element responds to blue light.